R,R,S,S-2-nitroimidazole derivatives

ABSTRACT

PCT No. PCT/JP93/01519 Sec. 371 Date Jul. 18, 1994 Sec. 102(e) Date Jul. 18, 1994 PCT Filed Oct. 21, 1993 PCT Pub. No. WO94/14778 PCT Pub. Date Jul. 7, 1994.High purity 2-nitroimidazole derivatives having excellent radiosensitivity and high safety and useful as a drug to be used along with radiotherapy of various cancers can be prepared at a high yield from inexpensive diester of tartaric acid according to the following reaction formua,   &lt;IMAGE&gt; and R2 may be the same or different and each individually represents an aliphatic group or an aromatic group, and X represents a halogen atom.

This application is a 371 of PCT/JP 93/01519 filed Oct. 20, 1993.

FIELD OF TECHNOLOGY

The present invention relates to an optically active 2-nitroimidazolederivative which is useful as a drug used along with radiotherapy ofcancers, a radiosensitizer comprising the same as an effectivecomponent, a process for preparing the same, and an intermediate for thepreparation of this derivative.

BACKGROUND ART

A 2-nitroimidazole derivative represented by the following formula (5)exhibits an action of promoting radiosensitivity of hypoxic cellsexisting in cancers. Because it has the excellent radiosensitivity andis highly safe, this compound is known to be useful as a drug used alongwith radiotherapy of cancer (Japanese Patent Application Laid-open(kokai) No. 223258/1991). ##STR2##

A process of the following reaction scheme is known for preparing the2-nitroimidazole derivative (5). ##STR3##

This process comprises a step of selectively acylating three hydroxygroups, two primary hydroxy groups and one secondary hydroxy group,among four hydroxy groups in erythritol which is a raw materialcompound. It is essential to react erythritol at a low temperature inorder to differentiate the reactivities of the primary hydroxy group andthe secondary hydroxy group. But at such a low temperature, a largeamount of solvent is required, because this raw material is scarcelysoluble. Further, because the reaction product from this step is amixture containing tetra-, tri-, di- and mono-acylated compounds, andunreacted compound, purification by column chromatography or the like isindispensable in order to selectively obtain the target triacylatedcompound. The low yield of this step results in the decrease in theoverall yield of the process. In addition, expensive raw materials suchas D-erythritol and L-erythritol must be used in order to produce theoptically active 2-nitroimidazole derivative.

The 2-nitroimidazole derivative (5) has two asymmetric carbon atoms.Isolation of the optical isomers is so difficult that there have been noreports on the successful isolation of these isomers. Furthermore,nothing have been known at all about the pharmaceutical activities ofthese optical isomers.

An object of the present invention is therefore to provide opticalisomers of 2-nitroimidazole derivative (5) and a drug comprising thesame as an effective components.

Other objects of the present invention is to provide a novel process forthe preparation of the 2-nitroimidazole derivative (5) and anintermediate for preparing this compound.

DISCLOSURE OF THE INVENTION

In view of this situation, the present inventors have undertakenextensive studies, and found that 2-nitroimidazole derivative and itsoptical isomers can be obtained at a high yield and industrialadvantage, by using tartaric acid diester which is an inexpensivecompound as a raw material and by producing an intermediate compound,2-halomethoxy-1,3,4-triacyloxybutane, by the ring-opening reaction of adioxolane compound. This finding has led to the completion of thepresent invention.

Specifically, the present invention provides optically active2-nitroimidazole derivatives of the following formulas (1) to (4) and aradiosensitizer comprising one of these derivatives as an effectivecomponent. ##STR4##

Furthermore, the present invention relates to a process for thepreparation of the 2-nitroimidazole derivative according to thefollowing reaction scheme, ##STR5## wherein R¹, R², and R³ may be thesame or different and each individually represents an aliphatic group oran aromatic group, and X represents a halogen atom; and to anintermediate for the 2-nitroimidazole derivative.

Specifically, the present invention relates to a process for preparing2-halomethoxy-1,3,4-triacyloxybutane derivative (11) comprising reacting1,3-dioxolane derivative (9), which is easily obtained from tartaricacid diester (6), and acyl halide (10).

Further, the present invention relates to a process for preparing2-nitroimidazole derivative (12), which comprises reacting the2-halomethoxy-1,3,4-triacyloxybutane derivative (11) and2-nitroimidazole.

Still further, the present invention relates to a process for preparing2-nitroimidazole derivative (5), which comprises reacting the2-halomethoxy -1,3,4triacyloxybutane derivative (11) and2-nitroimidazole, and deacylating the thus-obtained compound (12).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be illustrated according to the reactionscheme presented above.

As aliphatic groups represented by R¹, R², and R³ in the above reactionscheme, linear, branched, or cyclic alkyl or alkenyl groups having 1-24carbon atoms are given. Specific examples include methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, n-octyl, and palmityl groups. Asexamples of aromatic groups, phenyl group, naphtyl group, and the likeare given. Fluorine, chlorine, bromine, and iodine atoms are given ashalogen atoms represented by X.

The reaction for producing compound (7) from compound (6) is preferablycarried out by adding phosphorous pentoxide to a mixture of compound (6)and dimethoxymethane, in portions, at room temperature or under heating.

The reaction for producing compound (8) from compound (7) comprises thecyclization of compound (7) by the reaction with a Lewis acid. Borontrifluoride, boron trifluoride etherate, anhydrous zinc chloride,anhydrous aluminum chloride, anhydrous tin chloride, and the like aregiven as Lewis acids to be reacted with compound (7). The reaction ofcompound (7) and Lewis acid is carried out by adding a catalytic amountto equivalent amount of Lewis acid to compound (7) at room temperatureor under heating while stirring. The reaction of compound (6) anddimethoxymethane may proceed until 1,3-dioxolane derivative (8) isproduced by the cyclization reaction, which partially occurs by theaction of phosphorous pentoxide. The cyclization reaction may be carriedout without separating this 1,3-dioxolane derivative (8) by adding Lewisacid to the reaction mixture.

In order to cyclize a diol compound to produce a 1,3-dioxolane compound,para-formaldehyde, 1,3,5-trioxane, or the like is generally used. In thecase of compound (6) these reagents can hardly produce the 1,3-dioxolanering, resulting in an extremely low yield. The above method, however,can produce 1,3-dioxolane derivative (8) from compound (6) at a highyield of greater than 90%.

The reaction for obtaining compound (9) from compound (8) can be carriedout by reducing compound (8) and reacting the reduced product with analiphatic or aromatic carboxylic acid or a reactive derivative thereof.

A reducing agent such as lithium aluminum hydride or sodium boronhydride can be preferably used for the reducing reaction. Acid halides,acid anhydrides, and the like can be given as examples of the reactivederivatives of aliphatic or aromatic carboxylic acid. The acylationreaction can be carried out preferably according to the conventionalmethod, for example, in the presence of a base such as pyridine at roomtemperature or under heating.

The reaction of the thus-obtained 1,3-dioxolane derivative (9) and acylhalide (10) can be carried out either in the absence of a catalyst or inthe presence of a Lewis acid. This reaction may be also carried outusing a solvent or without using a solvent. Benzene, toluene,chloroform, dichloromethane, ethyl acetate, acetonitrile, or the likecan be used as a solvent, and anhydrous zinc chloride, anhydrous zincbromide, stannic chloride, anhydrous aluminum chloride, or the like canbe used as the Lewis acid. The reaction temperature is -30° C. to 100°C. Because this reaction is typically exothermic, it is preferablycarried out while cooling with water.

The reaction of 2-halomethoxy-1,3,4-triacyloxybutane derivative (11)thus obtained and 2-nitroimidazole is carried out preferably in thepresence of a base. Given as examples of the bases are inorganic basessuch as sodium carbonate, sodium hydrogen carbonate, potassiumcarbonate, potassium hydrogen carbonate, cesium carbonate, and sodiumhydride; and organic bases such as triethylamine, pyridine, andtributylamine. The reaction is usually carried out in an organicsolvent. As the solvents which can be used, polarized solvents such asmethanol, ethanol, i-propanol, tetrahydrofuran, dimethylformamide, anddimethylsulfoxide are given. The reaction temperature may be either lowor high, with room temperature being preferred.

The deacylation of compound (12) can be carried out according to theconventional method. The compound (5) which is useful as aradiosensitizer can be obtained by this deacylation reaction.

The deacylation reaction can be carried out by the method in whichcompound (12) is treated for several hours to overnight at 0° C. to roomtemperature in anhydrous alcohol containing sodium alcolate or inanhydrous alcohol saturated with ammonia gas; a method in which compound(12) is treated at room temperature to 80° C. in a water-alcohol mixtureor an organic base such as triethylamine or pyridine; or the like.

After the reaction, the target compound can be separated from thereaction mixture and purified according to conventional methods. Forexample, in order to separate and purify the target compound, thereaction mixture is concentrated and crystallized or, alternatively,extracted, washed, and concentrated following which the residue issubjected to chromatography or the like.

Compounds (7), (8), (9), (11), (12), and (5) with the stericconfiguration being retained can be obtained, if the optically activecompound (6) is used as the raw material for the reactions of thepresent invention.

Among the compound of formula (11), compounds of the following formula(11a) having aliphatic groups for R^(1') and R^(2') which correspond toR¹ and R² in formula (11), are novel compounds, on which there have beenno descriptions in published documents. ##STR6##

Among the optically active 2-nitroimidazole derivatives of the presentinvention, the compound represented by formula (1) can be prepared fromoptically active tartaric acid as a starting raw material according tothe following reaction formula, ##STR7## wherein R¹, R², and R³ have thesame meanings as previously defined. Specifically, D-(-)-tartaric aciddiester (6') is reacted with dimethoxymethane in the presence ofphosphorous pentoxide to produce compound (7'). The compound (7') iscyclized by the reaction with Lewis acid to obtain 1,3-dioxolanederivative (8'), which is reduced and acylated into compound (9'). Thiscompound (9') is then reacted with an acid anhydride in the presence ofLewis acid to produce compound (9"). The compound (9") is reacted with2-nitroimidazole to produce compound (12'), which is deacylated toobtain RR isomer (1).

Each step of the reaction scheme is then illustrated.

The reaction for producing compound (7') from D-(-)-tartaric aciddiester (6') can be preferably carried out by adding phosphorouspentoxide in portions to the mixture of the D-(-)-tartaric acid diester(6') and dimethoxymethane at room temperature or under heating.

The reaction for producing 1,3-dioxolane derivative (8') from compound(7') is a cyclization reaction in which compound (7') is reacted withLewis acid. Boron trifluoride, boron trifluoride etherate, anhydrouszinc chloride, anhydrous aluminum chloride, anhydrous tin chloride, andthe like are given as Lewis acids to be reacted with compound (7'). Thereaction of compound (7') and Lewis acid is carried out by adding acatalytic amount to equivalent amount of Lewis acid to compound (7') atroom temperature or under heating while stirring. The reaction ofcompound (6') and dimethoxymethane may proceed until 1,3-dioxolanederivative (8') is produced by the cyclization reaction, which partiallyoccurs by the action of phosphorous pentoxide. The cyclization reactionmay be completed without separating this 1,3-dioxolane derivative (8')by adding Lewis acid to the reaction mixture.

The reaction for producing compound (9') from 1,3-dioxolane derivative(8') is carried out by reducing the 1,3-dioxolane derivative (8') toobtain compound (8") and reacting this compound (8") with fatty acidanhydride.

A reducing agent such as lithium aluminum hydride or sodium boronhydride can be preferably used for the reducing reaction. The acylationreaction can be preferably carried out according to the conventionalmethod, for example, in the presence of a base such as pyridine at roomtemperature or under heating.

The reaction of compound (9") and acid anhydride is carried out in thepresence of a Lewis acid. Anhydrous zinc chloride, anhydrous zincbromide, stannic chloride, anhydrous aluminum chloride, or the like canbe used as the Lewis acid. This reaction may be carried out using asolvent or without using a solvent. Benzene, toluene, chloroform,dichloromethane, ethyl acetate, acetonitrile, or the like can be used asthe solvent. Although the reaction may be carried out either at a lowtemperature or under heating, room temperature is usually preferred.

The reaction of compound (9") thus obtained and 2-nitroimidazole iscarried out in the presence of an acid catalyst by melting thesecompounds while the pressure is being reduced. As the acid catalyst usedin this reaction, protonic acids, such as p-toluenesulfonic acid,methanesulfonic acid, and trichloroacetic acid; and Lewis acids, such asanhydrous zinc chloride, anhydrous aluminum chloride, and anhydrouscupric chloride, can be given. The proportion of compound (9") and2-nitroimidazole used in the reaction can be arbitrarily determined.Usually, a small excess amount of the former is preferably used. Apreferable reaction temperature is usually 50°-150° C., with thereaction time usually between 30 minutes to 6 hours depending on thereaction reagents, solvents, temperature, the type of the acid catalyst,and the like.

The deacylation of compound (12') can be carried out, for example, bythe method in which compound (12') is treated for several hours toovernight at 0° C. to room temperature in anhydrous alcohol containingsodium alcolate or in anhydrous alcohol saturated with ammonia gas, amethod in which compound (12') is hydrolyzed at room temperature orunder heating in a water-alcohol mixture or in an organic base such astriethylamine or pyridine, or the like. A lower alcohol such asmethanol, ethanol, or propanol are preferably used as the alcohol.

Among the optically active 2-nitroimidazole derivatives of the presentinvention, the compound represented by formula (2) can be prepared byusing L-(+)-tartaric acid diester instead of D-(-)-tartaric acid diester(6'), as a starting raw material, according to the above reactionformula.

Further, among the optically active 2-nitroimidazole derivatives, thecompounds represented by formulas (3) and (4) can be prepared by usingmeso-tartaric acid diester instead of D-(-)-tartaric acid diester (6'),as a starting raw material, according to the above reaction formula.Alternatively, these may be prepared by benzoylating the three hydroxygroups of racemic 2-nitroimidazole derivative (5) which is obtained bythe method described in Japanese Patent Application Laid-open (kokai)No. 110675/1989 and optically resolving the resulting tribenzoatecompound, followed by debenzoylation.

The benzoylation of the racemic 2-nitroimidazole derivative (5) can beachieved at a high yield by acting benzoyl chloride in the presence of abase such as pyridine while stirring at room temperature. The racemictribenzoate isomers obtained here are optically resolved by HPLC using achiral column to produce the optically active tribenzoate compound.Debenzoylation can be carried out by a method comprising hydrolysis atroom temperature in a water-alcohol mixture in the presence of anorganic base such as triethylamine, or the like method.

After the reaction, the target compound can be separated from thereaction mixture and purified according to conventional methods. Forexample, in order to separate and purify the target compound, thereaction liquid is extracted, washed, and concentrated, following whichthe residue is subjected to chromatography or the like.

The compounds (1) to (4) of the present invention thus obtainedexhibited low toxicity and excellent in vivo and in vitroradiosensitizing activity as shown in test examples hereinafter, andthus are useful as a radiosensitizer to be used in radiotherapy ofcancers.

It is preferable that the radiosensitizer of the present invention beadministered five minutes to five hours prior to the time when radiationis given to a subject. Either oral or non-oral administration isacceptable. The composition can be prepared into tablets, capsules,granules, powder, suppositories, or injection, after the addition ofsuitable additives such as excipients, stabilizers, preservatives, andbuffering agents. A dose is dependednt on the age, location of cancers,types of cancers, symptoms, and the like, with an amount of 0.2 to 5g/m² body surface area being usually preferable.

EXAMPLES

The present invention is hereinafter illustrated more specifically byway of examples, which should not be construed as limiting the presentinvention.

Example 1 Synthesis of diethyl (S,S)-bis(O-methoxymethyl)tartarate

25.76 g of diethyl D-(-)-tartarate was mixed with and completelydissolved in 50 ml of dimethoxymethane. Phosphorous pentoxide was addedto the solution in portions while stirring at room temperature to effectthe reaction. While monitoring the reaction by TLC (developer, CHCl₃:CH₃ OH=19:l; detection by iodine), phosphorous pentoxide was addeduntil a single spot of Rf 0.88 developed. After the reaction, thereaction mixture was transferred to a separating funnel and extractedwith 700 ml of a 5:1 mixed solution of ethyl acetate and benzene. Theextract was washed with water and saturated aqueous solution of sodiumchloride, dried over anhydrous sodium sulfate, and filtered, followed byremoval of the solvent by evaporator to obtain the title compound as anoily substance.

MS: 294(M⁺)

NMR(CDCl₃)δ:

1.30(6H, t, --OCH₂ CH₃ ×2),

3.34(6H, s, --OCH₃ ×2),

4.16-4.30(4H, m, --OCH₂ CH₃ ×2),

4.66-4.79(6H, m, >CHO--×2 and --OCH₂ OCH₃ ×2)

Example 2 Synthesis of (4S,5S)-4,5-bis(ethoxycarbonyl)-1,3-dioxolane

To a solution of 30.07 g of diethyl (S,S)-bis(O-methoxymethyl)tartarateobtained in Example 1 in 300 ml of benzene was added 16.12 g of borontrifluoride etherate, and the mixture was stirred at room temperature toreact. After the reaction overnight, the reactant was extracted with theaddition of 500 ml of ethyl acetate. The extract was neutralized withsaturated aqueous solution of sodium hydrogen carbonate, washed withwater and saturated aqueous solution of sodium chloride, and dried overanhydrous sodium sulfate. After filtration, the solvent was evaporated.Although it was possible to use this product as is for the nextreaction, the title compound was obtained almost quantitatively as acolorless transparent oil when purified by silica gel columnchromatography.

MS: 218(M⁺)

NMR(CDCl₃)δ:

1.31(6H, t, --CH₂ CH₃ ×2),

4.26(4H, q, --CH₂ CH₃ ×2),

4.76(2H, s, >CHO--×2),

5.26(2H, s, --OCH₂ O--×2)

Example 3 Synthesis of (4R,5R)-4,5-bis(hydroxymethyl)-1,3-dioxolane

300 ml of diethyl ether was added to 25.75 g of lithium aluminumhydride, and the mixture was heated while refluxing. A solution of130.46 g of (4S,5S)-4,5-bis (ethoxycarbonyl)-1,3-dioxolane (obtained inExample 2) in 100 ml of ether was slowly added dropwise to this mixture.After the addition, the refluxing was continued for further about onehour. After allowing the reaction mixture to cool, 30 ml of water wasslowly added under ice-cooling to decompose an excessive amount oflithium aluminum hydride. Then, 30 ml of 4N aqueous solution of sodiumhydroxide and 90 ml of water were added dropwise. The reaction mixturewas filtered with suction and the precipitate was extracted with 1000 mlof an ethanol-dioxane mixture at about 60° C., followed by filtration ofthe extract with suction. This procedure was repeated three times. Thefiltrate was concentrated to obtain crude(4R,5R)-4,5-bis(hydroxymethyl)-1,3-dioxolane.

Example 4 Synthesis of (4R,5R)-4,5-bis(acetoxymethyl)-1,3-dioxolane

The crude (4R,5R)-4,5-bis(hydroxymethyl)-1,3dioxolane obtained inExample 3 was dissolved in 300 ml of pyridine. After the addition of 150g of excessive amount of acetic anhydride under ice cooling, the mixturewas reacted for about 16 hours while stirring at room temperature. 20 mlof ethanol was added in portions while cooling over a water bath inorder to decompose the excessive amount of acetic anhydride. Afterconcentration by evaporator, the concentrate was extracted with 500 mlof ethyl acetate and washed with water, followed by removal of thesolvent by evaporator. Although this product may be used for the nextreaction as it was, the purification by silica gel column chromatographyafforded 79.29 g of light yellow oil of(4R,5R)-4,5-bis(acetoxymethyl)-1,3-dioxolane.

MS: 218(M⁺)

NMR(CDCl₃)δ:

2.11(6H, s, --COCH₃ ×2),

4.00-4.04(2H, m, >CHO--×2),

4.21-4.23(4H, d, --CH₂ OCO--×2),

5.06(2H, s, --OCH₂ O--)

Example 5 Synthesis of (2R,3R)-2-bromomethoxy-1,3,4-triacetoxybutane

A mixture of 25.0 g of acetyl bromide and 42.0 g of(4R,5R)-4,5-bis(acetoxymethyl)-1,3-dioxolane obtained in Example 4 wasstirred under cooling with ice, and 1.0 g of anhydrous zinc chloride wasadded to it. After the reaction for 30 minutes, the ice water bath wasdismantled and the mixture was stirred for a further one hour whilestirring at room temperature. After the reaction, 50 ml of benzene wasadded to separate insoluble matters by filtration, and the benzene wasevaporated at a low temperature (below room temperature). No peaks forthe raw material were observed at all by NMR analysis of the reactionproduct, indicating that the decylization occurred quantitatively andthe title compound was produced.

NMR(CDCl₃)δ:

2.0-2.2(9H, --COCH₃ ×3),

4.0-4.4(5H, --CH₂ OAc ×2, >CHOCH₂ --),

5.3(1 H, >CHOCO--),

5.7-5.8(2H, --OCH₂ Br)

Example 6 Synthesis of (1'R,2'R)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazole

21.5 g of 2-nitroimidazole, 20.0 g of triethylamine, and 50 ml ofdimethylformamide were added to all the amount of the crude(2R,3R)-2-bromomethoxy-1,3,4-triacetoxybutane obtained in Example 5. Thereaction was exothermic, producing white precipitate of triethylaminehydrobromide. The mixture was cooled to control the reaction temperaturebelow 40° C. The reaction was continued for a further several hours atroom temperature while stirring. The produced hydrobromide was filteredwith suction and the precipitate was washed with ethyl acetate. Thefiltrate and washings were combined and concentrated by evaporator.After evaporating almost all dimethylformamide, the residue wasextracted with the addition of ethyl acetate. The ethyl acetate layerwas washed thoroughly with saturated aqueous solution of sodium hydrogencarbonate until there was no yellow color of 2-nitroimidazole. Thisproduct was then washed with water, dried, concentrated, and purified bysilica gel column chromatography (eluent: 9:1 mixture of benzene andethyl acetate) to obtain 49.7 g (yield: 70.0%) of the title compound.

MS: 373(M⁺)

NMR(CDCl₃)δ:

2.0-2.2(9H, --COCH₃ ×3),

4.0-4.4(5H, m, --CH₂ OCO--×2, >CHOCH₂ --),

5.1-5.2(1H, m, >CHOCO--),

5.8-6.1(2H, nq, --OCH₂ N (ring)),

7.2-7.3(d×2, ring proton)

Example 7 Synthesis of (1'R,2'R)-1-[(2',3'-dihydroxy-1'-hydroxymethyl)propoxy]methyl-2-nitroimidazole

11.58 g of(1'R,2'R)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazoleobtained in Example 6 was dissolved in 100 ml of methanol and themixture was stirred at room temperature. 10 ml of triethylamine and 20ml of water were added to effect the hydrolysis while stirring. Afterconfirming the completion of the reaction by TLC (developer:chloroform:methanol=9:1; detection by UV absorption), the solvent wasevaporated and the residue was crystallized. The crystals wererecrystallized from ethanol to obtain 4.30 g of yellowish white crystalsof the title compound.

m.p.: 99°-101.5° C.

MS(m/e): 248(M+1)

NMR(DMSO)δ:

3.25-3.33(2H, m, --CH(OH)CH₂ OH),

3.39-3.64(4H, m, --CH×2 and --CH(OCH₂ --)CH₂ OH),

4.46(1H, t, --CH(OH)CH₂ OH),

4.59(1H, --CH(OH)--),

4.64(1H, --CH(OCH₂ --)CH₂ OH),

5.88(2H, nq, --CH₂ N (ring)),

7.21(1H, S, ring proton),

7.83(1H, S, ring proton)

IR(cm⁻¹): 3385(OH), 1540(NO₂), 1370(NO₂)

Optical rotation: [α]_(D) ²⁵ =-12.09° (c=1.0, MeOH) [α]_(D) ²⁰ =-9.2°(c=2.0, H₂ O)

Example 8 Synthesis of(2RS,3SR)-2-acetoxy-3-bromomethoxy-1,4-dibenzoyloxybutane

34.2 g of (4RS,5SR)-4,5-bis(benzoyloxymethyl)-1,3-dioxolane and acetylbromide were mixed with stirring under cooling with ice. The mixture wasfurther reacted with the addition of 1.0 g of zinc bromide. Afterdismantling the ice water bath, 50 ml of dichloromethane was added andreacted while stirring at room temperature. After the reaction for twohours, the insoluble matters were separated by filtration, and thefiltrate was concentrated by evaporator at a low temperature (below roomtemperature) to obtain the title compound.

NMR(CDCl₃)δ:

4.0-4.7(5H, m, --CH₂ OBz×2, >CHOCH₂),

5.2(1H, m, >CHOCO--),

5.7(2H, s, --OCH₂ Br),

7.2-8.1(10H, m, Aromatic)

Example 9 Synthesis of (1'S,2'S)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazole

17.0 g of (2S,3S)-2-bromomethoxy-1,3,4-triacetoxybutane, 5.7 g of2-nitroimidazole, 8.8 g of potassium carbonate, and 100 ml of ethylalcohol were mixed and reacted at room temperature overnight whilestirring. The insoluble matters were separated by filtration, thefiltrate was concentrated by evaporator, and 100 ml of ethyl acetate wasadded to the residue, followed by mixing. After separating the insolublematters by filtration, the filtrate was washed thoroughly with saturatedaqueous solution of sodium hydrogen carbonate until there was no yellowcolor of 2-nitroimidazole. This product was then washed with water anddried. After evaporating the solvent, the residue was purified by silicagel column chromatography (eluent: 9:1 mixture of benzene and ethylacetate) to obtain 7.9 g

(yield: 43.0%) of the title compound.

MS: 373(M⁺)

NMR(CDCl₃)δ:

2.0-2.2(9H, s×3, --COCH₃ ×3),

4.0-4.4(5H, m, --CH₂ OCO--×2, >CHOCH₂ --),

5.1-5.2(1H, m, --CH--OCO--),

5.8-6.1(2H, nq, --OCH₂ N (ring)),

7.2-7.3(d×2, ring proton )

Example 10 Synthesis of (1'S,2'S)-1-[(2',3'-dihydroxy-1'-hydroxymethyl)propoxy]methyl-2-nitroimidazole

68.9 g of (1'S,2'S)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazole obtained in Example 9 wasmixed with and dissolved in 200 ml of methanol. After the addition of100 g of triethylamine, the mixture was stirred at room temperature.Then, 30 ml of water was added, followed by stirring overnight to effectthe hydrolysis. After confirmation of completion of the reaction by TLC(developer: ethyl acetate, detection by UV), the reaction mixture wasconcentrated by evaporator. The concentration by evaporation wasrepeated with the addition of isopropanol and toluene, until theproduced acetic acid and triethylamine were completely removed. Theresidue was dissolved in 50 ml of ethanol, filtered through glassfilter, and crystallized with the addition of crystal seeds. Afterseparation by filtration, the crystals were dried to obtain 26.2 g(yield: 57.0%) of the title compound as light yellow crystals.

m.p.: 97°-98° C.

MS: 248(M⁺)

NMR(DMSO)δ:

3.2-3.7(6H, m, --CH₂ OH×2, >CHO--×2),

4.50(1H, t, --CH₂ OH),

4.6-4.7(2H, m, --CH₂ OH and >CHOH),

5.85(2H, nq, --OCH₂ N (ring)),

7.18(1H, d, ring proton),

7.80(1H, d, ring proton)

Optical rotation: [α]_(D) ²⁵ =+12.2° (c=1.0, CH₃ OH) [α]_(D) ²⁰ =+9.4°(c=2.0, H₂ O)

Optical purity: 99.5% ee

Elemental analysis

Found (%): C;16.93 H;38.88 N;5.35

Calculated (%): C;17.00 H;38.87 N;5.30

Example 11 Synthesis of (2R,3R)-2-acetoxymethoxy-1,3,4-triacetoxybutane

100 ml of acetic anhydride was added to 70.12 g of(4R,5R)-4,5-bis(acetoxymethyl)-1,3-dioxolane obtained in Example 4 andmixed at room temperature to dissolve. After the addition of 3.05 g ofanhydrous zinc chloride and 10 ml of glacial acetic acid, the mixturewas stirred overnight. The resultant reaction mixture was extracted with700 ml of ethyl acetate, neutralized with saturated aqueous solution ofsodium hydrogen carbonate, washed with water and saturated aqueoussolution of sodium chloride, dried over anhydrous sodium sulfate, andfiltered. The solvent was removed by evaporation to obtain 99.48 g ofthe title compound as a reddish brown oil.

MS: 320(M⁺)

NMR(CDCl₃)δ:

2.07(3H, s, --COCH₃),

2.09(3H, s, --COCH₃),

2.01(3H, s, --COCH₃),

2.12(3H, s, --COCH₃),

4.04-4.38(5H, m, --CH₂ OCO×2 and >CHOCH₂ --),

5.21-5.27(1H, m, >CHOCO--),

5.31(2H, s, --OCH₂ O--)

Example 12 Synthesis of diethyl (2R,3R)-bis(O-methoxymethyl)tartarate

20.6 g of diethyl L-(+)-tartarate was mixed with and completelydissolved in 60.8 g of dimethoxymethane. The mixture was reacted withthe addition of phosphorous pentoxide in portions while stirring at roomtemperature. While monitoring the reaction by TLC (developer,benzene:ethyl acetate=3:2; detection by iodine), phosphorous pentoxidewas added until a single spot of Rf 0.63 developed. After the reaction,the supernatant was transferred to a separating funnel and extractedwith 200 ml of ethyl acetate. The extract was washed with saturatedaqueous solution of sodium hydrogen carbonate, and then water severaltimes, dried, concentrated by evaporator, and purified by silica gelcolumn chromatography (eluent: benzene) to obtain 23.7 g (yield: 80.8%)of the title compound.

MS: 294(M⁺)

NMR(CDCl₃)δ:

1.32(6H, t, --CH₃ ×2),

3.35(6H, s, --OCH₃ ×2),

4.25(4H, m, --CH₂ CH₃ ×2),

4.6-4.9(6H, m, --OCH₂ OCH₃ ×2 and >CHOCH₂ --×2)

Example 13 Synthesis of (4R,5R)-4,5-bis(ethoxycarbonyl)-1,3-dioxolane

23.7 g of diethyl (2R,3R)-bis(O-methoxymethyl)tartarate obtained inExample 12 was dissolved in 50 ml of benzene and reacted with theaddition of 11.5 g of boron trifluoride etherate while stirring. Afterthe reaction overnight at room temperature, the resultant reactionmixture was transferred to a Separating funnel and extracted with 200 mlof ethyl acetate. The extract was neutralized with saturated aqueoussolution of sodium hydrogen carbonate, washed with water, dried, andconcentrated by evaporator. Although it was possible to use this productas it was for the next reaction, the product was purified by elutingwith benzene using silica gel column to obtain 17.6 g (yield: 99.8 g) ofthe title compound.

MS: 218(M⁺)

NMR(CDCl₃)δ:

1.35(6H, t, --CH₂ CH₃ ×2),

4.30(4H, q, --CH₂ CH₃ ×2),

4.75(2H, s, >CHO--×2),

5.25(2H, s, --OCH₂ O--)

Example 14 Synthesis of (4S,5S)-4,5-bis(hydroxymethyl)-1,3-dioxolane

300 ml of tetrahydrofuran was added dropwise to 43.61 g of lithiumaluminum hydride while cooling with ice. To this was added dropwise asolution of 125.3 g of (4R,5R)-4,5-bis(ethoxycarbonyl)-1,3-dioxolaneprepared in Example 13 in 200 ml of tetrahydrofuran and reacted whilevigorously stirring under cooling with ice. After the addition, themixture was reacted for one hour while refluxing. Then, water was addeddrop by drop to hydrolyze lithium aluminum hydride under cooling withice. After the addition of 0.5 ml of 4 mol/l sodium hydroxide dropwise,the mixture was stirred for 30 minutes and filtered with suction. 700 mlof ethanol was added to the precipitate, and the mixture was heated at60°-70° C., stirred, and filtered with suction. This procedure wasrepeated three times. All filtrates were combined and concentrated byevaporator to obtain a crude title compound.

Example 15 Synthesis of (4S,5S)-4,5-bis(acetoxymethyl)-1,3-dioxolane

200 ml of pyridine was added to crude(4S,5S)-4,5-bis(hydroxymethyl)-1,3-dioxolane obtained in Example 14 todissolve the latter. An excessive amount of acetic anhydride (200 g) wasadded dropwise under cooling with ice. After several hours of reaction,ethyl alcohol was added dropwise to decompose the excessive aceticanhydride. The reaction mixture was concentrated by evaporator to removealmost all pyridine. The concentrate was extracted with the addition of500 ml of ethyl acetate. The extract was washed with saturated aqueoussolution of sodium hydrogen carbonate, then with water, dried, andconcentrated by evaporator. The residue was purified by silica gelcolumn chromatography (eluent, benzene:ethylacetate=9:1) to obtain 90.0g of the title compound as a colorless liquid.

MS: 218(M⁺)

NMR(CDCl₃)δ:

2.10(6H, s, CH₃ CO--×2),

4.02(2H, m, >CHO--×2),

4.25(4H, m, --CH₂ CO--×2),

5.05(2H, s, --OCH₂ O--)

Example 16 Synthesis of (2S,3S)-2-acetoxymethoxy-1,3,4-triacetoxybutane

100.2 g of acetic anhydride was added to 61.0 g of(4S,5S)-4,5-bis(acetoxymethyl)-1,3-dioxolane obtained in Example 15. Tothis was added 11.8 g of glacial acetic acid to dissolve the mixture.3.4 g of anhydrous zinc chloride was added while stirring. The zincchloride was slowly dissolved to change the color of the mixture fromyellow into charcoal. After the reaction overnight, the reaction mixturewas charged into a separating funnel which contained 500 ml of ethylacetate. To this was added saturated aqueous solution of sodium hydrogencarbonate to neutralize. After washing with water and drying, theproduct was concentrated by evaporator. Acetic anhydride not decomposedwas removed by a chemical pump to obtain 91.9 g (yield: 87.7%) of anyellow oil of the title compound.

MS: 320(M⁺)

NMR(CDCl₃)δ:

2.05-2.15(12H, s×4, CH₃ CO--×4),

4.1-4.4(5H, m, --CH₂ O--×2, >CHOCH₂ --),

5.25(1H, m, >CHOCO--),

5.35(2H, s, --OCH₂ O--)

Example 17 Synthesis of diethyl (2RS,3SR)-bis(O-methoxymethyl)tartarate

20.6 g of diethyl meso-tartarate was mixed with and completely dissolvedin dimethoxymethane. The mixture was reacted with the addition ofphosphorous pentoxide in portions while stirring at room temperature.While monitoring the reaction by TLC (developer, benzene:ethylacetate=3:2; detection by iodine), phosphorous pentoxide was added untila single spot of Rf 0.62 was developed. After the reaction, the reactionmixture was transferred to a separating funnel and extracted with 200 mlof ethyl acetate. The extract was washed with saturated aqueous solutionof sodium hydrogen carbonate, and then with water, dried over anhydroussodium sulfate, and filtered. The solvent was removed by evaporator toobtain the title compound as an oily substance.

MS: 294(M⁺)

NMR(CDCl₃)δ:

1.35(6H, t, --OCH₂ CH₃ ×2),

3.45(6H, s, --OCH₃ ×2),

4.1-4.4(4H, m, --OCH₂ CH₃ ×2),

4.6-4.9(6H, m, >CHO--×2 and --OCH₂ OCH₃ ×2)

Example 18 Synthesis of (4RS,5SR)-4,5-bis(ethoxycarbonyl)-1,3-dioxolane

29.4 g of diethyl (2RS,3SR)-bis(O-methoxymethyl)tartarate obtained inExample 17 was dissolved in 100 ml of benzene and reacted with theaddition of 14.2 g of boron trifluoride etherate while stirring at roomtemperature. After the reaction overnight, the resultant reactionmixture was extracted with 200 ml of ethyl acetate. The extract wasneutralized with saturated aqueous solution of sodium hydrogencarbonate, washed with water, dried over anhydrous sodium sulfate, andfiltered, followed by evaporation of the solvent. Although it waspossible to use this product as it was for the next reaction, theproduct was purified by silica gel column chromatography toquantitatively obtain the title compound as a colorless transparent oil.

MS: 218(M⁺)

NMR(CDCl₃)δ:

1.35(6H, t, --CH₂ CH₃ ×2),

4.25(4H, q, --CH₂ CH₃ ×2),

4.80(2H, s, >CHO--×2),

5.2(1H, s, --OCH₂ O--),

5.4(1H, s, --CH₂ O--)

Example 19 Synthesis of (4RS,5SR)-4,5-bis(hydroxymethyl)-1,3-dioxolane

100 ml of tetrahydrofuran was added to 11.4 g of lithium aluminumhydride, and the mixture was heated while refluxing. To this was addeddropwise a solution of 21.8 g of(4RS,5SR)-4,5-bis(ethoxycarbonyl)-1,3-dioxolane prepared in Example 18in 30 ml of tetrahydrofuran. After the addition, the mixture was reactedfor one hour while refluxing. After allowing to cool, 30 ml of water wasslowly added while cooling with ice to hydrolyze excessive lithiumaluminum hydride. Then, 30 ml of 4N aqueous solution of sodium hydroxideand 90 ml of water was added dropwise. The mixture was filtered withsuction, following which the precipitate was extracted with 1000 ml ofethanol-dioxane mixture at 60° C. and filtered with suction. Thisprocedure was repeated three times. All filtrates were concentrated byevaporator to obtain a crude title compound.

Example 20 Synthesis of (4RS,5SR)-4,5-bis(acetoxymethyl)-1,3-dioxolane

(4RS,5SR)-4,5-bis(hydroxymethyl)-1,3-dioxolane obtained in Example 19was dissolved in 100 ml of pyridine. An excessive amount of aceticanhydride (30.6 g) was added under cooling with ice. After reacting forabout four hours at room temperature, 10 ml of ethyl alcohol was addeddropwise under cooling with ice to decompose the excessive aceticanhydride. The reaction mixture was concentrated by evaporator. Theconcentrate was extracted with the addition of 300 ml of ethyl acetate,the extract was washed with water, and the solvent was removed byevaporator. Although it was possible to use this product in the nextstep as it was, the residue was purified by silica gel columnchromatography (eluent, benzene:ethylacetate=95:5) to obtain 18.5 g(yield: 85.0%) of the title compound as a light yellow oil.

MS: 218(M⁺)

NMR(CDCl₃)δ:

2.15(6H, s, --COCH₃ ×2),

4.1-4.2(2H, m, >CHO--×2),

4.3-4.4(4H, d, --CH₂ OCO ×2),

4.9(1H, s, --OCH₂ O--),

5.2(1H, s, --OCH₂ O--)

Example 21 Synthesis of(2RS,3SR)-2-acetoxymethoxy-1,3,4-triacetoxybutane

20 ml of acetic anhydride was added to 12.2 g of(4RS,5SR)-4,5-bis(acetoxymethyl)-1,3-dioxolane obtained in Example 20.The mixture was mixed to dissolution at room temperature. To this wereadded 0.7 g of anhydrous zinc chloride and 2 ml of glacial acetic acid.The mixture was stirred overnight at room temperature and extracted with300 ml of ethyl acetate. The extract was neutralized with saturatedaqueous solution of sodium hydrogen carbonate. After washing with waterand drying over anhydrous sodium sulfate, the product was filtered andthe solvent was evaporated to obtain 19.0 g (yield: 92.0%) of the titlecompound.

MS: 320(M⁺)

NMR(CDCl₃)δ:

2.08(3H, s, --COCH₃),

2.09(3H, s, --COCH₃)

2.10(3H, s, --COCH₃),

2.11(3H, s, --COCH₃),

4.1-4.5(5H, m, --CH₂ OCO ×2 and >CHOCH₂ --),

5.1-5.2(1H, m, >CHO--CO--),

5.32(2H, q, --OCH₂ O--)

Example 22 Synthesis of (1'RS,2'SR)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazole

8.4 g of 2-nitroimidazole and a catalytic amount (0.2 g) ofpara-toluenesulfonic acid were added to 23.8 g of(2RS,3SR)-2-acetoxymethoxy-1,3,4-triacetoxybutane obtained in Example21. The mixture was slowly heated with stirring, while removing aceticacid produced in the reaction by suction using an aspirator. The aceticacid started to evaporate at the oil bath temperature of 80°-90° C. Theevaporation almost terminated at 140° C. indicating the completion ofthe reaction, whereupon the reaction mixture was allowed to cool andextracted with 100 ml of a solvent. The extract was washed thoroughlywith saturated aqueous solution of sodium hydrogen carbonate until therewas no yellow color in washings due to 2-nitroimidazole. Then, theproduct was washed with water, dried over anhydrous sodium sulfate, andfiltered. The solvent was evaporated and the residue was purified bysilica gel column chromatography (eluent, benzene:ethylacetate=9:1) toobtain 13.8 g (yield: 50.0%) of light yellow oil of the title compound.

MS: 373(M⁺)

NMR(CDCl₃)δ:

2.03(3H, s, --CH₃)

2.05(3H, s, --CH₃),

2.08(3H, s, --CH₃),

3.95-4.50(5H, m, --CH₂ OCO ×2 and >CHOCH₂ --),

5.05-5.15(1H, m, >CHOCO--),

5.90(2H, s, >CHOCH₂ --),

7.20(1H, s, ring proton),

7.30(1H, s, ring proton)

Example 23 Synthesis of (1'RS,2'SR)-1-[(2',3'-dihydroxy-1'-hydroxymethyl)propoxy]methyl-2-nitroimidazole

6.9 g of (1'RS,2'SR)-1-[(1'-acetoxymethyl-2',3'-diacetoxy)propoxy]methyl-2-nitroimidazole obtained in Example 22 wasdissolved in 30 ml of methanol, and stirred at room temperature. Afterthe addition of 10 ml of triethylamine and 5 ml of water, the mixturewas stirred to effect the hydrolysis. After confirmation of completionof the reaction by TLC (developer: ethyl acetate, detection by UV), thesolvent was evaporated and the residue was crystallized. 2.6 g (yield:57.0%) of yellow crystals of the title compound was obtained byrecrystallization from ethanol.

m.p.: 136.0°-137.0° C.

MS: (m/e): 284(M+1)

NMR(DMSO)δ:

3.15-3.70(6H, m, --CH(OH)CH₂ OH, --CH×2 and --CH(OCH₂ --)CH₂ OH),

4.40(1H, t, --CH(OH)CH₂ OH),

4.75(1H, d--CH(OH)--),

4.65(1H, t, --CH(OCH₂ --)CH₂ OH),

5.85(2H, s, --OCH₂ N (ring)),

7.15(1H, s, ring proton),

7.80(1H, s, ring proton)

IR(cm⁻¹): 3385(OH), 1540(NO₂), 1370(NO₂)

Example 24 Synthesis of (1'R,2'S)/(1'S,2'R)-1-[(1'-benzoyloxymethyl -2',3'-dibenzoyloxy)propoxy]methyl-2-nitroimidazole

100 ml of pyridine was added to 4.59 g of (1'RS, 2'SR)-1-[(2',3'-dihydroxy-1'-hydroxymethyl) propoxy]-methyl-2-nitroimidazole preparedin Example 23. To the mixture was added dropwise 10 ml of benzoylchloride while stirring over a water bath. After stirring overnight, thesolvent was evaporated and the residue was extracted with 500 ml of a4:1 mixture of ethyl acetate and benzene. The extract was washed withwater, d-HCl, saturated aqueous solution of sodium hydrogen carbonate,water, and saturated aqueous solution of sodium chloride, dried overanhydrous sodium sulfate, and filtered. The solvent was evaporated andthe residue was purified by silica gel column chromatography(benzene-ethyl acetate) to obtain a quantitative amount of the titlecompounds as a light yellow oil.

These compounds were optically resolved by HPLC using a chiral column(AS 0.46 φ×2.5L) to isolate the optically active compounds (tribenzoatecompounds of formulas (3) and (4)).

MS: 559(M⁺)

NMR(CDCl₃)δ:

3.42-4.85(5H, m, --CH₂₀ CO×2 and --CH(OCH₂ --)CH₂ --),

5.68-5.73(1H, m, --CH(OCO--)CH₂ --),

5.95-6.07(2H, nq, --OCH₂ N (ring)),

7.00(1H, d, imidazole ring proton),

7.27(1H, d, imidazole ring proton),

7.39-7.48(6H, m, m-benzene ring proton),

7.53-7.62(3H, m, p-benzene ring proton),

7.93-8.02(6H, m, o-benzene ring proton)

Example 25 Synthesis of (1'R,2'S)/(1'S,2'R) -1-[(2',3'-dihydroxy-1'-hydroxymethyl)propoxy]propoxy]methyl-2-nitroimidazole

15.99 g of one of the optically resolved compounds among(1'R,2'S)/(1S,2'R)-1-[(1'-benzoyloxymethyl-2',3'-dibenzoyloxy)propoxy]methyl-2-nitroimidazole of Example 24 wasdissolved in 150 ml of ethanol and 10 ml of ethyl acetate, and thesolution was stirred at room temperature. To the mixture were added 50ml of water and 15 ml of triethylamine, followed by stirring to effecthydrolysis. After confirmation of completion of the reaction by TLC(developer: chloroform:methanol =19:1), the solvent was evaporated andthe residue was crystallized. Another resolved compound was also treatedin the same manner to obtain crystals. These were respectivelyrecrystallized to obtain the title compounds as white needles.

m.p.: 129°-130.5° C.

MS: 248(M+1)

NMR(DMSO)δ:

3.16-3.63(6H, m, >CHO--×2 and --CH₂ OH×2),

4.22(1H, t, --CH(OH)CH₂ OH),

4.95(1H, t, --CH(OCH₂ --)CH₂ OH),

4.68(1H, d, --CHOH--),

5.83(2H, nq, --OCH₂ N (ring)),

7.19(1H, d, ring proton),

7.78(1H, d, ring proton)

Optical rotation: (1'R*, 2'S*): [α]_(D) ²⁰ =+4.7° (c=2, H₂ O) (1'S*,2'R*): [α]_(D) ²⁰ =-4.5° (c=2, H₂ O)

IR(cm⁻¹): 3315(OH), 1545(NO₂), 1365(NO₂)

Test Example 1 In vitro hypoxic cell sensitization effect

The SR-RS racemate is known to exhibit about the same degree of hypoxiccell radiosensitization effect as misonidazole (Japanese PatentApplication Laid-open (kokai) No. 223258/1991). The degree of thehypoxic cell radiosensitization effects of optical isomers of thepresent invention as compared with the racemate was studied by the invitro assay.

Specifically, the radiosensitization effects were investigated usingbreast carcinoma cell EMT6/KU derived from Balb/c mouse. A hypoxic cellsuspension was prepared from MEM suspension-containing EMT6/KU cells ata concentration 4×10⁵ cells/ml by adding the test compound to a finalconcentration of 1 mM, and gently shaking it under a nitrogen gas streamcontaining 5% CO₂ for one hour at room temperature. Gamma-ray wasirradiated to the suspension and a radiation-survival rate curve wasdeveloped by the colony formation method. The sensitization rate wasdetermined from this radiation-survival rate curve by dividing (i) theamount of radiation which decreases the survival rate of the hypoxiccells by 1% when no test compound was added by (ii) the amount ofradiation which decreases the survival rate of the hypoxic cells by 1%when the test compound was added. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                           Hypoxic cell                                               Sample             sensitization rate                                         ______________________________________                                        RS-SR racemate     1.7                                                        SS isomer          1.8                                                        RR isomer          1.8                                                        RS or SR isomer (rotation(+))                                                                    1.7                                                        RS or SR isomer (rotation(-))                                                                    1.7                                                        ______________________________________                                    

As can be seen in Table 1, the optical isomers of the present inventionhave the same degree of excellent hypoxic cell radiosensitizationeffects as the racemate, indicating their effectiveness for theradiation therapy of cancer.

Test Example 2 In vivo-in vitro hypoxic cell sensitization effect

The degree of the hypoxic cell radiosensitization effects of opticalisomers of the present invention in in vivo-in vitro system wasinvestigated in the same manner using the racemate as a control.Specifically, the radiosensitization effects were investigated usingEMT6/KU-cancerated Balb/c mouse. 200 mg/kg of each test compound wasadministered and 20 Gy gamma-ray was irradiated 30 minutes thereafter.Carcinoma was extracted and treated with trypsin to prepare a cellsuspension. The survival rate was determined by the colony formingmethod. A physiological saline solution was administered to the control.The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                           Hypoxic cell                                               Sample             survival rate (%)                                          ______________________________________                                        No radiation, physiological                                                                      36.21                                                      saline administered                                                           Radiation, physiological                                                                         0.81                                                       saline administered                                                           RS-SR racemate     0.08                                                       SS isomer          0.07                                                       RR isomer          0.07                                                       RS or SR isomer (rotation(+))                                                                    0.08                                                       RS or SR isomer (rotation(-))                                                                    0.08                                                       ______________________________________                                    

As can be seen in Table 2, the optical isomers of the present inventionhave the same degree of excellent hypoxic cell radiosensitizationeffects as the racemate, indication their effectiveness for theradiation therapy of cancer.

Test Example 3 (Dissolution test)

Solubilities of SS, RR, SR, and RS isomers and SR-RS racemate in waterand physiological saline were determined. The results are shown in Table3.

                  TABLE 3                                                         ______________________________________                                                              Solubility in                                                        Solubility in                                                                          physiological                                                        water (g/ml)                                                                           saline (g/ml)                                           ______________________________________                                        SS isomer      0.85       0.82                                                RR isomer      0.74       0.87                                                RS or SR isomer                                                                              N.A.       0.07                                                (rotation(+))                                                                 RS or SR isomer                                                                              N.A.       0.06                                                (rotation(-))                                                                 SR-RS racemate 0.04       0.04                                                ______________________________________                                    

As can be seen from the results shown in Table 3, the solubilities ofSS, RR, SR, and RS isomers are remarkably larger than that of SR-RSracemate. This indicates a great advantage of the compounds of thepresent invention in that the amount of aqueous carriers can be greatlyreduced in injection, a conceivable ideal form for a hypoxic cellradiosensitizer of which a dose must be a large amount.

Test Example 4 Determination of octanol-phosphate partition coefficient

The partition coefficient in the octanol-phosphate buffer solutionsystem, which is indicative of the degree of orientation toward nervetissues, was determined. Amounts of 1.4 times and 0.7 times thesolubility in octanol of each sample were precisely weighed. To theweighed samples 10 ml of 0.2 mol phosphate buffer (pH 7.4), defined inthe Pharmacopoeia of Japan, and 10 ml of octanol were added. Themixtures were shaken for 24 hours at 20° C. under light shielding.Octanol and phosphate layers were partitioned to determine theabsorbance of each layer. The partition coefficients at 1.4 and 0.7times the solubility in octanol were determined from the ratio of theabsorbances. The partition coefficients obtained were averaged todetermine the partition coefficient of each sample. The results areshown in Table 4.

                  TABLE 4                                                         ______________________________________                                                                     partition                                                   1.4 times                                                                              0.7 time coefficient                                      ______________________________________                                        SS isomer    0.026      0.031    0.028                                        RR isomer    0.024      0.026    0.025                                        RS or SR isomer                                                                            0.053      0.059    0.056                                        (rotation(+))                                                                 RS or SR isomer                                                                            0.048      0.058    0.053                                        (rotation(-))                                                                 SR-RS racemate                                                                             0.037      0.057    0.047                                        Misonidazole 0.378      0.401    0.390                                        ______________________________________                                    

As clear from the results shown in Table 4, among the optically activeisomers SS isomer and RR isomer are less partitioned toward the octanollayer, and are thus less exhibitive of nerve toxicity.

Test Example 5 (Acute toxicity test)

Test compounds, dissolved in physiological saline or a physiologicalsaline solution containing 10% DMSO, were intravenously orintraperitoneally injected to ICR male mice, aged 5 weeks. The mice wereobserved for 14 days after the injection to determine the median lethaldose (LD_(50/14)). The results are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        Compound of the  LD.sub.50/14                                                 present invention                                                                              (mg/kg)                                                      ______________________________________                                        Compound (1)     6,000                                                        Compound (2)     6,000                                                        Compound (3)     5,900                                                        Compound (4)     5,900                                                        ______________________________________                                    

Test Example 6 (Acute toxicity test)

The acute toxicity was determined using groups of male ICR mice, aged 5weeks, each group consisting of five mice. Test compounds were dissolvedin physiological saline and administered by injection through caudalvein. The death-survival determination was made 14 days after theadministration. The results in terms of dead animals/tested animals arein Table 6.

                  TABLE 6                                                         ______________________________________                                                    Dose (mg/kg)                                                                  3000      6000   9000                                             ______________________________________                                        SS isomer     0/5         1/5    5/5                                          RR isomer     0/5         3/5    N.A.                                         SR isomer     0/5         3/5    N.A.                                         RS isomer     0/5         3/5    N.A.                                         SR-RS racemate                                                                              0/5         3/5    N.A.                                         ______________________________________                                    

As clear from the results shown in Table 6, SS isomer exhibited bettersafety than other optically active isomers.

Test Example 7 (Acute toxicity test)

Exhibition of toxicity of SR-RS racemate and SS isomer were tested byintravenous injection (500 mg) to beagle dogs. The results are shown inTable 7.

                  TABLE 7                                                         ______________________________________                                                    Exhibition of toxicity                                            ______________________________________                                        SR-RS racemate                                                                              The dog vomited 60, 80, 90 minutes                                            after the injection                                             SS isomer     The dog exhibited no change in 24                                             hours after the injection                                       ______________________________________                                    

As clear from the results shown in Table 7, the SS isomer exhibitedremarkably suppressed nerve toxicity as compared with the SR-RSracemate.

Industrial Applicability

High purity 2-nitroimidazole derivatives can be prepared at a high yieldfrom inexpensive diester of tartaric acid by the present invention. The2-nitroimidazoles obtained exhibit excellent radiosensitivity and highsafety. The compounds are thus suitable as a drug to be used along withradiotherapy of various cancers.

We claim:
 1. A 2-nitroimidazole derivative represented by any one of thefollowing formulas (1) or (2), ##STR8##
 2. The compound of claim 1 whichis ##STR9##
 3. The compound of claim 1 which is ##STR10##
 4. Aradiosensitizer composition comprising a radiosensitizer effective mountof the compound of claim 1, in non-racemic form and in substantiallyoptically pure form and a carrier.
 5. The composition of claim 4 whereinthe compound of claim 1 is a compound having formula
 1. 6. Thecomposition of claim 4 wherein the compound of claim 1 is a compoundhaving formula
 2. 7. The composition of claim 5, wherein the compound offormula 1 has a solubility in water of about 0.74 g/ml.
 8. Thecomposition of claim 6, wherein the compound of formula 2 has asolubility in water of about 0.85g/ml.
 9. The compound of claim 1 offormula (2) having an optical purity of 99.5%.